Battery operated direct current motors are increasingly being used as a drive in handheld work apparatus such as, for example, chain saws, hedge trimmers, brushcutters, blowers, cut-off machines or the like.
In order to be able to use lightweight, high powered electric motors, a substantial electronic outlay has to be implemented. The electric motors are operated close to their maximum power range, which is why sophisticated electronic monitoring is used with which an electric overloading of the motor is avoided and equally an overloading of the power electronics is avoided. For this, a plurality of operating data of the electric motor must be captured and evaluated, usually with microprocessors. For this, each signal is supplied to an input of the processor, which is why a processor must have a plurality of, in particular, analog inputs in order to process all the signals in an adapted manner. Processors having a plurality of inputs, in particular analog inputs, are cost intensive and require a lot of space.
If electronically commutated electric motors are used, defined starting conditions must be given for starting so that the electronically commutated rotating field drives the rotor in the intended rotational direction. Defined operating conditions are also necessary when running up the motor to operating rotational speed. It must be ensured that the rotor can reliably follow the rotating field which is becoming faster. Thus, the motor can be operated during start-up by ramping up according to fixedly predetermined switching sequences. In order to ensure a reliable starting of an electronically commutated electric motor, for example position sensors are arranged which detect the rotational position of the rotor and convey the same to the electronic control unit of the motor. Thus, Hall sensors, for example, are used with which it can be ensured that the rotating field is always switched in a manner adapted to the rotational position of the rotor. If the operating rotational speed has been reached, the rotating field is controlled on the basis of the voltages induced in the motor in the field windings of the stator, whose magnitude and direction ensure a reliable control of the electronically commutated electric motor in the region of the operating rotational speed.
Aside from the generator voltage of the rotating electric motor, other operating signals are also detected, for example the load current, which can also be used for the control of the rotating field. Because the generator voltage is in the volt range and the load voltage, which is indicative of a load current, is in the millivolt range, the operating signals must be separately processed and supplied to the control unit separately.
The electronic complexity for operating an electronically commutated motor is considerable; the microprocessors used already process a multiplicity of supplied signals, which is why the use of further operating signals of the motor is often problematic or not possible without the replacement of the processor with a larger and more cost-intensive processor with more analog inputs.